The use of contact lenses involves a daily disinfecting treatment, and numerous and varied soaking and sterilization processes have been proposed.
Certain commercial compositions have as a base disinfecting agents, such as sodium mercurothiolate or chlorhexidine salts. According to U.S. Pat. No. 3,689,673, hydrophilic flexible contact lenses are treated by soaking in an aqueous containing from 0.001 to 0.1% chlorohexidine for a sufficient time and a sterilization is obtained in two to three hours with a solution of 0.001% concentration and in thirty minutes at a concentration of 0.01%.
At the present time, these disinfecting products are no longer used, because they have the drawback of facilitating the creation of deposits on the contact lenses.
Flexible, or soft, contact lenses are generally made from hydrophilic polymers. Now, the hydroxy groups of the lenses attract and retain substantial amounts of water in the plastic and this results in drawbacks during cleaning and sterilization. Moreover, additional difficulties are encountered in the treatment of hydrophilic flexible contact lenses because of their tendency to complex and concentrate certain preservatives used for conventional lenses, such as chlorobutanol, benzalkonium chloride, thimerosal, phenylmercuric nitrate . . . which are generally inactivated in the complex state. If the concentrated preservatives are released too quickly on the cornea, they can cause chemical burns. Consequently, the cleaning solutions presently available for conventional hard lenses are not suitable for flexible contact lenses.
The effectiveness of hydrogen peroxide as a disinfectant and its use as a germicidal agent in the disinfecting of numerous apparatuses and devices for medical use are well known.
Since 1972, hydrogen peroxide has been indicated as an advantageous agent in the sterilization of contact lenses as noted on page 247 of "Soft Contact Lens", published by C. V. Mosby Co., St. Louis. The majority of the products presently used have an aqueous solution base of hydrogen peroxide in a concentration on the order of 3%.
However, before a flexible contact lens is introduced into the eye, it must be rinsed several times in an isotonic buffered solution with a pH of 6.9 to 7.1. A correct rinsing, consisting of repeated immersions and rinsings, i.e. up to four, takes time--on the order of thirty or more minutes--, large volumes of saline solution and, depending on the user, gives no certainty of reproducibility. Further, the rinsing simply dilutes the hydrogen peroxide to a weaker concentration. Hydrogen peroxide, even in very small amounts on the order of about 10 ppm (parts per million) can cause eye irritation.
Consequently, processes for removal of hydrogen peroxide from flexible contact lenses have been studied. French Patent No. 2.231.395 proposes a process for treatment of a flexible contact lens to perform its cleaning and sterilization and to treat it for its introduction into the eye after a complete sterilization, comprising placing the flexible contact lens in an aqueous sterilization solution having a hydrogen peroxide base containing an approximately isotonic concentration of sodium chloride and a catalytic amount of a decomposition catalyst for the hydrogen peroxide and in maintaining the contact lens in said solution until the concentration of hydrogen peroxide present is less than about 10 ppm. The flexible contact lens is thus effectively treated and sterilized by exposure to the action of the hydrogen peroxide for a period of ten minutes. However, the flexible contact lenses are then left in this aqueous solution of hydrogen peroxide for about six hours. By operating under these conditions the lenses are sterilized and the amount of detectable residual hydrogen is 20 ppm; to reduce the amount to less than 10 ppm, a single rinsing in the isotonic saline solution suffices.
European Patent No. 0 110 609 proposes a sterilizing treatment with hydrogen peroxide associated with the neutralization of the residual amounts of hydrogen peroxide with a solution of sodium pyruvate. The lenses are contacted with the hydrogen peroxide for at least about 5 minutes, preferably 10 minutes. They are then immersed in the sodium pyruvate solution, then washed with an isotonic aqueous sterile solution.
It has been found that hydrogen peroxide is not very effective in the sterilization of contact lenses, particularly as a fungicide. Additionally, certain deposits on the lenses are attributable to the presence of microorganisms.
French Patent No. 2.247.327 relates to the cleaning and restoration of plastic objects, particularly contact lenses. According to this process of complex practice, the lens is alternately made to undergo an expansion and a contraction to contribute to the removal of the residues and dirty marks. The ocular lens is put successively in contact with a first aqueous acid solution containing a peroxocompound, then with a second basic aqueous solution containing a peroxocompound, the the lens is put in contact with a non-ionic detergent and subjected to rinsing with water. The first and second solutions contain 0.1 to 15% by weight of a peroxocompound used for its great ability for cleaning and bleaching.